1. Field of the Invention
This invention relates generally to a system and method for providing turn-to-turn short circuit detection in the stator of an alternator and, more particularly, to a system and method for providing turn-to-turn short circuit detection in the stator of a vehicle alternator by determining a speed of the alternator, determining an alternator ripple current frequency in a rectified alternator current or voltage signal, determining a winding ripple current frequency from the alternator ripple current frequency, determining an amplitude of the winding ripple current frequency and comparing the amplitude to an estimated amplitude.
2. Discussion of the Related Art
Vehicles typically include an alternator that provides electrical power to recharge a vehicle battery and operate the vehicle electrical systems when the vehicle is running. The alternator includes a pulley that engages a flexible belt driven by the vehicle engine, where the belt also drives other vehicle components, such as a power steering pump, an air compressor, etc. As the belt rotates the alternator pulley, the pulley rotates a rotor within a stator of the alternator, where the rotor typically has a permanent magnet and the stator includes one or more wound coils. A typical vehicle alternator will include three stator windings that are 90° out-of-phase with each other that generate three AC signals that are sent to a three-phase diode bridge rectifier to convert the AC signals to a DC signal suitable for recharging the battery. The alternator will also include a voltage regulator that regulates the DC signal. The diode bridge rectifier generates an AC ripple signal on the DC signal as a factor of the conversion. Various filtering techniques and other operations can be performed to reduce the ripple current generated by the rectifier conversion, but there still will be some level of AC ripple on the DC signal that can be detected.
As mentioned above, the stator of a vehicle alternator includes a number of windings, which are typically narrow wires enclosed by insulation that prevents the wires from being in electrical contact with each other and short circuiting. Through operation of the vehicle and otherwise, sometimes the insulation of the wires can be damaged, which may cause a short circuit between the wires, referred to in the industry as a turn-to-turn short fault. Also, it is possible that the windings can be short circuited to ground, which also has the same undesirable effect as the turn-to-turn short fault. If such a turn-to-turn short fault occurs in one of the windings, then that particular phase of the alternator will have a reduced output current, depending on the number of windings that are involved in the short circuit, which reduces the torque of the alternator. Further, if one of the phases has a lower output current, then the alternator may become unbalanced, which may cause vibrations. Further, if the turn-to-turn short fault is significant enough, the alternator may overheat, which could damage alternator components, such as the alternator core.
Currently, there does not exist a technique for detecting a turn-to-turn short fault in a vehicle alternator. However, in other industries, it is known to detect a turn-to-turn short circuit of related electrical machines, most notably high voltage AC machine. For example, it is known to detect a high frequency current within an electrical machine caused by a partial discharge due to winding insulation damage. In another technique, the voltage and current of each winding phase is measured in the electrical machine and are compared to each other to detect a negative current sequence indicating a turn-to-turn short circuit. Yet another technique uses frequency spectrum analysis to detect a turn-to-turn short circuit in an electrical machine, but also requires phase voltage and current measurements from each of the windings. Another technique to detect a turn-to-turn short in an electrical machine monitors the motor control signals to detect a fault signature that will occur by the control signals trying to compensate for the short circuit.
All of the above described techniques require measurement of the phase voltage and current of the windings in the electrical machine. Because these measurements require sensors, it is an added cost to an automotive application that is undesirable.